Back to EveryPatent.com
| United States Patent |
5,514,938
|
|
Zaaijer, deceased
, et al.
|
May 7, 1996
|
D.C. ciruit for starting high pressure discharge lamp
Abstract
A circuit arrangement for igniting and operating a discharge lamp (La),
provided with
input terminals (K1,K2) for connection to a DC voltage source,
a commutator (COM) coupled to the input terminals and provided with
terminals (K3,K4) for connecting the discharge lamp (La), for cornmutating
a current through the discharge lamp (La),
a branch A which is conducting in both directions at least for alternating
current, of which branch a first end is connected to an input terminal
(K2) and a further end is connected to the commutator (COM), and which
branch comprises an inductive element L shunted by a branch B which
comprises a unidirectional element (D),
a branch C which connects a further input terminal to the commutator (COM),
and
an ignition circuit (S) for igniting the discharge lamp. According to the
invention, the unidirectional element (D)is so included in the branch B
that the branch B conducts a current at least immediately after ignition
of the discharge lamp (La). It is achieved thereby that a lamp operated by
means of the circuit arrangement has good take-over properties.
The invention relates to a circuit arrangement for igniting and operating a
discharge lamp, provided with
input terminal for connection to a DC voltage source,
a commutator coupled to the input terminals and provided with terminals for
connecting the discharge lamp, for commutating a current through the
discharge lamp,
a branch A which is conducting in both directions at least for alternating
current, of which branch a first end is connected to an input terminal and
a further end is connected to the commutator, and which branch comprises
an inductive element L shunted by a branch B which comprises a
unidirectional element,
a branch C which connects a further input terminal to the commutator, and
an ignition circuit for igniting the discharge lamp.
| Inventors:
|
Zaaijer, deceased; Gerrit J. (late of Eindhoven, NL);
Kunnen, legal representative; by Henricus J. (Valkenswaard, NL)
|
| Assignee:
|
U.S. Philips Corporation (New York, NY)
|
| Appl. No.:
|
328306 |
| Filed:
|
October 24, 1994 |
Foreign Application Priority Data
| Current U.S. Class: |
315/291; 315/200R; 315/224; 315/308; 315/310; 315/DIG.7 |
| Intern'l Class: |
G05F 001/00 |
| Field of Search: |
315/291,200 R,224,226,253,265,272,283,307,308,DIG. 7,DIG. 5,310
|
References Cited
U.S. Patent Documents
| 4748381 | May., 1988 | Ganser et al. | 315/200.
|
| 4775822 | Oct., 1988 | Statnic et al. | 315/224.
|
| 4887007 | Dec., 1989 | Almering et al. | 315/224.
|
| 5369339 | Nov., 1994 | Reijnaerts | 315/224.
|
| 5369340 | Nov., 1994 | Leyten | 315/307.
|
| 5414327 | May., 1995 | Reijnaerts | 315/224.
|
| Foreign Patent Documents |
| 8901224 | Dec., 1990 | NL.
| |
Primary Examiner: Lee; Benny
Assistant Examiner: Philogene; Haissa
Attorney, Agent or Firm: Blocker; Edward
Claims
It is claimed:
1. A circuit arrangement for igniting and operating a discharge lamp, said
circuit arrangement comprising:
(a) first and second input terminals for connection to a DC voltage source,
said first input terminal being negatively poled,
(b) a commutator coupled to the input terminals for commutating a current
through the discharge lamp,
(c) a branch A having first and second ends and which is capable of
conducting in both directions at least for alternating current, said
branch A first end being connected to a first input terminal, said branch
A second end being connected to the commutator, said branch A further
comprising an inductive element L shunted by a branch B, said branch B
further comprising a unidirectional element having cathode and anode
electrodes,
(d) a branch C connecting the second input terminal to the commutator,
(e) an ignition circuit for igniting the discharge lamp, characterized in
that:
(f) the cathode of the unidirectional element in branch B is connected to
the first input terminal and the anode of the unidirectional element is
connected to the commutator such that the branch B conducts current at
least immediately after ignition of the discharge lamp.
2. A circuit arrangement for igniting and operating a discharge lamp as
claimed in claim 1, wherein the branch B comprises an impedance element
connected in series with the unidirectional element.
3. A circuit arrangement for igniting and operating a discharge lamp as
claimed in claim 2, wherein the impedance element comprises an ohmic
resistor.
4. A circuit arrangement for igniting and operating a discharge lamp as
claimed in claim 1, further comprising a branch Z connecting branch A and
branch C and comprising voltage-limiting means.
5. A circuit arrangement for igniting and operating a discharge lamp as
claimed in claim 4, wherein the voltage-limiting means comprises a zener
diode.
6. A circuit arrangement for igniting and operating a discharge lamp as
claimed in claim 1, wherein the discharge lamp is a high pressure
discharge lamp.
7. A circuit arrangement for igniting and operating a discharge lamp as
claimed in claim 1, wherein the discharge lamp is a xenon high-pressure
lamp.
Description
BACKGROUND OF THE INVENTION
Such a circuit arrangement is known from published Netherlands Patent
Application 8901224. The circuit arrangement described therein is
particularly suitable for operating high-pressure discharge lamp, referred
to as lamp hereinafter. The current through the lamp is low-frequency
commutated during stationary lamp operation. The lamp as a result has a
luminous efficacy which is substantially equal to the luminous efficacy
obtained when the lamp is operated with a direct current, while
overheating of the electrodes in the lamp is avoided. The inductive
element L serves as a short-circuit protection: if there is a
short-circuit in the commutator, the inductive element L limits the
current supplied by the DC voltage source. The unidirectional element in
branch B renders it possible for electromagnetic energy stored in the
inductive element L during a short-circuit to be dissipated in branch B. A
disadvantage of the known circuit arrangement is that the current flowing
from the DC voltage source through the lamp immediately after lamp
ignition is comparatively weak. This comparatively weak current is a
result of the face that the unidirectional element is so connected that it
cannot conduct part of the lamp current. The full lamp current flows
through the inductive element, so that the speed with which the lamp
current rises immediately after lamp ignition is limited. This limited
current through the lamp immediately after lamp ignition causes a bad
take-over, or possibly even lamp extinction. Take-over is here understood
to mean the phase in lamp operation between lamp ignition and the moment a
stable discharge between the electrodes is achieved.
SUMMARY OF THE INVENTION
The invention has for its object inter alias to provide a circuit
arrangement which achieves a good take-over of the lamp after lamp
ignition.
According to the invention, this object is achieved in that the
unidirectional element is so included in the branch B that the branch B
conducts a current at least immediately after ignition of the discharge
lamp.
It was found that discharge lamps of the high-pressure discharge lamp type
operated on a circuit arrangement according to the invention show a very
good take-over behavior.
It was also found to be advantageous that the branch B comprises an
impedance connected in series with the unidirectional element. Favorable
results were obtained with embodiments of a circuit arrangement according
to the invention in which this impedance comprises an ohmic resistor.
Depending on the dimensioning of the circuit arrangement and the properties
of the lamp operated on the circuit arrangement, it may be desirable to
limit the potential difference between branch A and branch C in that
branch A and branch C are connected by means of a branch Z which comprises
voltage-limiting means. Preferably, these voltage-limiting means comprise
a zener diode.
Embodiments of a circuit arrangement according to the invention will be
explained in more detail with reference to a drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawing, FIG. 1 is a diagram of an embodiment of a circuit
arrangement according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIG. 1, K1 and K2 are terminals for connection to a DC voltage source.
COM is a commutator built up from four switching elements S1, S2, S3 and
S4. A load Lo comprising a lamp La and a starter circuit S coupled to the
lamp La for igniting the lamp is connected to the commutator COM. The
coupling between La and S is indicated with a broken line in the FIGURE.
Input terminal K1 is connected to a first main electrode of switching
element S1. This connection in the present embodiment forms branch C.
Branch A is formed by the connection between input terminal K2 and a main
electrode of switching element S2. Coil L in this embodiment forms an
inductive element which forms pan of branch A. A series circuit of diode D
and ohmic resistor R in this embodiment forms branch B which is part of
branch A. Zener diode Ze in this embodiment forms branch Z, and at the
same time voltage-limiting means comprised in branch Z. A first side of
coil L is connected to input terminal K2 and also to a cathode of diode D.
An anode of diode D is connected to a first side of resistor R. A further
side of resistor R is connected to a further side of coil L and to an
anode of zener diode Ze. A cathode of zener diode Ze is connected to input
terminal K1. Zener diode Ze is shunted by a series circuit of switching
element S1 and switching element S2, and also by a series circuit of
switching element S3 and switching element S4. Control electrodes of the
switching elements S1 to S4 are connected to a control circuit (not shown)
which forms pan of the commutator COM. Terminal K3 is connected to a
common junction point of switching element S1 and switching element S2.
Terminal K4 is connected to a common junction point of switching element
S3 and switching element S4. Terminal K3 and terminal K4 are connected to
respective ends of the lamp La.
The operation of the circuit arrangement shown in FIG. 1 is as follows.
When input terminals K1 and K2 are connected to a DC voltage source, the
starter circuit S generates an ignition voltage which is present between
terminals connected to the lamp electrodes. A discharge is generated in
the lamp under the influence of the ignition voltage. If the lamp is a
high-pressure discharge lamp, lamp operation subsequent to lamp ignition
can be subdivided into three consecutive phases. During the first two
phases, the voltage across the lamp rises from a comparatively low value
to a value corresponding to stationary lamp operation. At the same time,
the current through the lamp changes from a comparatively strong current
to a current corresponding to stationary lamp operation. Lamp operation is
stationary in the third phase. In the first phase, in which the take-over
of the lamp takes place, immediately after the ignition has been achieved,
the impedance of the lamp is low and a comparatively strong current flows
through the lamp via the conducting switching elements, ohmic resistor R,
diode D and coil L during a comparatively short time interval. The
amplitude of this comparatively strong current is substantially fully
determined in a given lamp by the resistance value of the ohmic resistor
R. The voltage across the resistor R and the diode D governs the rate at
which the current through the coil L increases. This comparatively strong
lamp current during the first phase of lamp operation is important for
realizing a good take-over of the lamp. The portion of the lamp current
flowing through the coil L is substantially zero immediately after lamp
ignition and then rises gradually. To be able to supply the comparatively
strong lamp current during the first phase, the DC voltage source may be
provided, for example, with an output capacitor connected between input
terminals K1 and K2. In the beginning of the first phase, the
comparatively strong current is realized in that the capacitor discharges
itself through the lamp. During discharging of the capacitor the quantity
of current flowing through the coil L increases. When in a later stage of
the first phase the output capacitor has been partly discharged, the
comparatively strong current through the lamp may also be partly realized,
depending on the dimensioning of the circuit, in that the coil L carries
part of this current and allows no comparatively fast changes in this part
of the current. During the second phase, which is also called the run-up
of the lamp, and which takes much longer than the first phase, a current
flows through the lamp which is considerably weaker than that during the
first phase. The control circuit renders switching elements S1 and S4 and
switching elements S2 and S3, respectively, alternately conducting and
non-conducting. As a result, the commutator changes the direction of the
lamp current with low frequency in order to prevent overheating of the
lamp electrodes. During these commutations, however, the current through
the lamp becomes substantially zero, so that the lamp extinguishes and has
to be re-ignited. Since the temperature of the lamp is still comparatively
low during the second please of lamp operation, the DC voltage supplied by
the DC voltage source is insufficient for re-igniting the lamp
comparatively quickly. The coil L, however, carries a comparatively large
portion of the current through the lamp during the second phase of lamp
operation. As a result of this the coil L generates a voltage whenever the
current through the lamp is interrupted during a commutation owing to the
fact that the lamp does not re-ignite immediately. Thus the lamp can
re-ignite at a re-ignition voltage which is equal to the sum of the DC
voltage supplied by the DC voltage source and the voltage generated by the
coil L. This comparatively high re-ignition voltage leads to a
comparatively quick re-ignition of the lamp during commutations. In the
third phase, i.e. stationary lamp operation, lamp temperature is such that
the lamp re-ignites substantially immediately at the DC voltage supplied
by the DC voltage source.
It has thus become possible by means of a circuit arrangement according to
the invention to send a comparatively strong current through a lamp
operated on the circuit arrangement immediately after lamp ignition. It is
also possible to generate a re-ignition voltage during the second phase of
lamp operation at which the lamp re-ignites comparatively quickly during a
commutation. As a result of these two properties, a lamp operated on a
circuit arrangement according to the invention has good take-over
characteristics and also good run-up characteristics.
With the use of a practical embodiment of a circuit arrangement as shown in
FIG. 1, a xenon high-pressure lamp with a power rating of approximately
35; W was ignited by the starter circuit at a voltage of approximately 600
V. Immediately after ignition the voltage across the lamp was
approximately 20 V. During the first phase of lamp operation, which lasts
approximately 0.2 ms, a current pulse with an amplitude of approximately 8
A flowed through the lamp. During the second phase, the amplitude of the
current through the lamp dropped from approximately 2.6 A to approximately
0.4 A. During re-ignition of the lamp in the beginning of the second phase
of lamp operation, the DC voltage of approximately 40 V supplied by the DC
voltage source was augmented by voltage pulses generated by the coil L
with an amplitude of approximately 500 V The amplitude of the voltage
pulses generated by the coil decreased to substantially zero volts during
the lamp run-up. DURing stationary operation, the voltage across the lamp
was approximately 85 V and the current through the lamp approximately 0.4
A.
Top